题解 | #合法IP#

// 这题完全是面向测试用例开发
#include <cctype>
#include <iostream>
using namespace std;

int main() {
    string str1,str2,str3,str4,str;
    while (cin >> str) { // 注意 while 处理多个 case
        int pointCnt = 0;
        bool bisValid = true;
        for(auto it : str){
            if(it == '.'){
                pointCnt ++;
            }else if(!isdigit(it)){
                bisValid = false;
            }
        }
        if(pointCnt != 3){
            bisValid = false;
        }
        int pos = str.find('.');
        str1 = str.substr(0, pos);
        str = str.substr(pos + 1);

        pos = str.find('.');
        str2 = str.substr(0, pos);
        str = str.substr(pos + 1);

        pos = str.find('.');
        str3 = str.substr(0, pos);
        str4 = str.substr(pos + 1);
        
        if(str1 == "" || str2 == "" || str3 == "" || str4 == ""){
            bisValid = false;
        }else if(str1[0] == '0' && str1.length() != 1 ||
        str2[0] == '0' && str2.length() != 1 || 
        str3[0] == '0' && str3.length() != 1 ||
        str4[0] == '0' && str4.length() != 1 ){
            bisValid = false;
        }
        else if(stoi(str1) > 255 || stoi(str2) > 255 || 
            stoi(str3) > 255 || stoi(str4) > 255){
            bisValid = false;
        }else if(stoi(str1) < 0 || stoi(str2) < 0 || 
            stoi(str3) < 0 || stoi(str4) < 0){
            bisValid = false;
        }

        if(bisValid){
            cout << "YES" << endl;
        }else{
            cout << "NO" << endl;
        }
    }
}
// 64 位输出请用 printf("%lld")